Initial activation of unstimulated B cells represents a highly regulated process by which signs generated at the cell surface ultimately direct a change in the resting program of gene expression that promotes cell cycle progression. Dysfunction in these processes may be associated with the progression of malignant lymphomas and the onset of autoimmune dyscrasias. The long term goal of this project is to understand how receptor initiated cytosolic signal transduction results in transcriptional control by elucidating the regulation of transcription factor induction. In particular, the receptors for T-independent antigen, slg, and direct T-dependent influences, CD40, will be examined; differential reliance on protein kinase C indicates that the pathways leading from slg and from CD40 differ in important ways. In order to learn about cytosolic signaling events that specifically couple receptors to nuclear changes, induction of transcription factors that are particularly relevant to B cell growth control, NF-kappaB, c-Rel, and NF- AT, will constitute the read-out for these studies. (1) The hypothesis that differences in the intracellular signaling pathways utilized by slg and CD40 are reflected in differences in the subunit composition of induced transcription factors will be tested by contrasting the nature and composition of NF-kappaB and NF-AT induced as a result of triggering these receptors. This will be done by immunological means and by testing trans-activating activity. (2) The hypothesis that the CD40 and slg receptors utilize a nonoverlapping set of intermediates will be tested by elucidating the cytosolic signaling pathways that specifically link CD40 and slg to induction of NF-kappaB and c-Rel. This will be done by evaluating fusion proteins incorporating the cytoplasmic tail of CD40, by evaluating the effects of dominant negative and antisense reagents, by examining xid mice, and by determining post-translational modification of lkappaB in response to receptor signaling. The possibility that a TNFR-like pathway involving ceramide plays a role in CD4O mediated signaling will be evaluated. (3) The hypothesis that calcineurin is responsible for nuclear translocation of c-Rel through an effect on lkappaBBeta will be evaluated in experiments aimed at understanding the mechanism underlying pharmacologic immunosuppression of c-Rel induction by cyclosporin A/FK-506. This will be done by determining the level of control of c-Rel synthesis, by overexpressing c-rel, and by determining whether calcineurin influences a c-Re/lkappaBBeta complex. The results of these studies will provide a clearer understanding of the receptor specific signaling elements that direct transcription factor induction and will help identify control points that may be of use in re- establishing growth control in malignant lymphomatous dyscrasias, in altering or eliminating unwanted serological autoreactivity, and in positively influencing the course of desired immune responses.